1. Field of the Invention
The present invention relates to a system and device for dynamic method for asymmetry compensation in a storage read channel.
2. Description of the Related Art
During the read process in a data storage device, a read head is passed over a data record in order to convert pre-recorded data into an analog signal. For example, in a magnetic tape drive, a magneto-resistive read head (“MRRH”) is passed over a data record written as flux reversals on a magnetic tape. As the MRRH passes over the tape, the MRRH converts the flux reversals into an electrical analog signal that represents the data originally stored on the magnetic tape. An analog to digital converter (“ADC”) periodically samples the analog signal and converts the sampled analog signal to a digital input signal. The ADC typically samples and converts a plurality of digital input signals forming a digital waveform. A data storage device such as a magnetic media storage device processes the digital waveform to reconstruct the data that was originally written to the tape.
The data waveform is typically recorded as flux reversals on a magnetic media and is symmetric, such that if the MRRH was perfectly adjusted, the received analog signal would be symmetric about a known reference level. For example, the analog signal may be symmetric about a reference level of zero volts (0 V). Unfortunately, manufacturing inconsistencies and read head wear may cause the read head to generate an asymmetric analog signal from the magnetic media. The asymmetric analog signal is converted to a plurality of digital input signals forming an asymmetric digital waveform. The asymmetry in the digital waveform increases the probability that the data storage device will interpret the asymmetric digital input signal incorrectly, resulting in an increased number of data errors.
Data errors due to a read head generating an asymmetric analog signal may make the read head unsuitable for shipment in a magnetic media storage device, increasing the failure rate and manufacturing costs of the read head. In addition, as the read head wears over time, the analog signals generated by these worn read heads will become more asymmetric. This shortens the life of the read head and the data storage device, increases the probability of an uncorrectable read error, and increases warranty costs.
The copending and commonly assigned patent application entitled “Apparatus, System, and Method for Mitigating Signal Asymmetry”, by Evangelos S. Eleftheriou, Ernest S. Gale, Robert A. Hutchins, Glen A. Jaquette, and Sedat Oelcer, having U.S. application Ser. No. 10/966,531 and filed Oct. 15, 2004, provides a technique to mitigate asymmetry using a look-up module to convert a sample from the analog digital converter (ADC) to a modified signal having fewer asymmetry errors.
There is a need for further techniques in the art to reduce asymmetry related errors.